Aging is accompanied by a progressive decline in memory and cognitive function. Aging people also experience a deterioration of sleep quality and efficiency. Although it is widely acknowledged that sleep has a critical role in learning and memory, the link between age-related sleep disruption and memory deficits remains unclear. We have previously shown that learning-induced formation of new synaptic connections in the cortex represents structural changes correlated with long-term memory storage. Our preliminary data suggests that sleep promotes synapse formation and performance improvement after learning in young adult animals. Moreover, learning-induced synapse formation is reduced in the motor cortex of aged mice. Based on these findings, we hypothesize that age-related sleep impairment contributes to the reduction in learning-dependent synapse formation and behavioral improvement. In this application, we will test this hypothesis by combining in vivo imaging of synapse structure and function, recording and behavioral testing in the same animals. The proposal has two specific aims. In the first aim, we will examine the role of sleep in learning-dependent synapse remodeling and behavioral performance in young, middle-aged and old mice. This will test the hypothesis that the benefit of sleep in promoting synapse formation and memory encoding is diminished in older mice. In the second aim, we will use in vivo calcium imaging to determine whether sleep- dependent reactivation of task-related neurons is reduced in aging and whether such deficiency in sleep reactivation mediates learning-related synaptic deficits. The proposed project explores, for the first time, the role of sleep in age-related declie in learning and memory at the level of individual neurons and synapses in the living brain. Successful completion of the project will lay the foundation for future studies exploring the mechanisms by which sleep abnormalities contribute to cognitive dysfunction in neurological diseases such as Alzheimer's disease.